The present invention relates to the formation of transducers and more particularly to the formation of transducers utilizing heat-sensitive piezoelectric substrate.
Polyvinylidene fluoride (PVF.sub.2) has received considerable interest as a material for piezoelectric transducers in non-destructive testing applications such as acoustic emission and ultrasonic pulse echo testing, particularly from aircraft components under fatigue test. Such transducers are less brittle than ceramic piezoelectric transducers, and have other highly desirable properties. For further information, see Robinson, A. L. Flexible PVF.sub.2 Film: An Exceptional Polymer for Transducers, in Science, 200 (4348): p. 1371-1374, June 23, 1978. Higher frequency transducers are needed to detect smaller critical flaws, but at frequencies of 20 MHz and above, ceramic piezoelectrics are thin and fragile, a problem not encountered with PVF.sub.2. In addition, PVF.sub.2 can function at higher power levels than many ceramic piezoelectric elements without suffering dielectric breakdown and subsequent failure. PVF.sub.2 films have also been used as diaphragms for loudspeakers and earphones. One method that is utilized to make effective connections to PVF.sub.2 is to utilize an epoxy disposed between and attaching a conductor to a PVF.sub.2 film and a contiguous electrical conductive coating applied to adjacent portions to electrically connect them as shown in U.S. Pat. No. 4,339,683. However, such technique requires that conductive coatings and wire leads be formed and attached on opposite sides of the film to form an active transducer area therebetween. Positioning the electrical connection on both sides of the substrate obstructs adhesive fastening to operational structures and prevents utilization of such transducers in structures which physically require that they be adhesively fastened with a smooth strong bond line. The production of operational structures utilizing transducers with electrical connections on both sides are costly and time consuming since the connections must be made prior to mounting on the structure. Additionally, when the electrical connections are on both sides and one of such sides is attached to the structure it becomes increasingly difficult to prevent the leads from shorting to the structure.